Historic, archived document

Do not assume content reflects current
scientific knowledge, policies, or practices

N V^>

H^

ac V

. ■

£fj/ y^r

WW-

V N/

-

circular no. 90.

Issued June 18, 1907

United States Department of Agriculture, y <

BUREAU OF ENTOMOLOGY,

L. O. HOWARD, Entomologist and Chief of Bureau.

THE WHITE-PINE WEEVIL.*

By A. D. Hopkins,

In Charge of Forest Insect Investigations.

•

The Bureau of Entomology has been conducting systematic and eco-
nomic investigations of the weevils infesting the bark of the trunk and
terminal shoots of conifers in the United States, the results of which will be
published in the regular technical and popular bulletins; but since

Fig. 1.— White-pine weevil (Pissodes strobi): a, Adult, smaller figure natural size; b, larva, line at
left natural length ; c, pupa, small figure of adult showing natural size. (Original.)

these can not be issued in time to be of service this season, this circular
has been prepared to give the information which is of immediate prac-
tical importance in regard to one of the most destructive of these weevils.

THE INSECT AND ITS HABITS.

The white-pine weevil is a somewhat elongate, brownish snout beetle,
4 to 5 mm. in length, having the thorax and elytra marked with irreg-
ular spots of brown and white scales (fig. 1, a). The winter is passed
in the adult stage, evidently in the ground. The beetles come out of
their winter quarters and fly early in May, and after feeding for a few
days on the bark of the living white-pine terminal shoots deposit their

1 Pissodes strobi Peck; Order Coleoptera, Family Curculionid?e.

eggs in punctures in the bark of the shoot of the previous year's growth,
placing one or two eggs in a pit or cavity in the inner bark made by

the beak of the mother beetle. In
from six to ten days the eggs begin
to hatch into small white grubs
(larvae), which at first are usually
found in large numbers feeding
upon the inner bark and cambium
(see fig. 2). They usually work
downward and sometimes extend
their work into the bark of the
2-year-old stem and base of the
branches. By the time the larva?
have completed their development
(fig. 1, b) they are greatly reduced
in numbers by natural enemies and
other causes. The survivors bur-
row into the wood or pith of the
terminal and excavate individual
transformation cells, which they
line and cover with excelsior-like
borings. In these cells they trans-
form to pupa? (see fig. 1, c) and
adults, and during July and August
of the same year, when the adults
are fully matured, they bore their
way out and seek suitable places
in which to pass the winter.

LONG LIFE OF THE ADULT.

From recorded observations on
some species of Pissodes or bark
weevils by investigators in Europe,
and on representatives of other
allied forms in Europe and in this
county, it appears that an indi-
vidual adult ma3T live two or three
years and will deposit eggs each
year.

SEASONAL HISTORY.

Pig. 2.- White-pine weevil : Newly hatched larvae The beetles are active from about
at work in vigorous terminal shoot of white the lgt to the 15th 0f May Or later,
pine. (Author's illustration.) .

depending on local conditions and
weather. Eggs are evidently deposited during the principal activity of
the adults, possibly during the greater part of the month of May. The

3

period of development of the larvae varies greatly. Those more fortu-
nate in securing a continuous food supply may become fully developed
before some of the less fortunate ones in the same terminal are one-
fourth as large, although the eggs from which both came may have been
deposited at about the same time. There is also a wide range in the
period of transformation to the pupa and adults and again in the emer-
gence of the latter. Thus, if the first eggs are deposited about the 8th
of May at Milford, Pa., latitude 41° 20', altitude 500 to 1,000 feet, the
first eggs will begin to hatch about the 14th of May, the first larvae will
be full grown about July 8, the first transformations to the pupae will
take place about the 15th of July, the first adults will begin to emerge
about July 25, and adults will continue to come out until the first part
of September. Practically all will be out by September 15. The prin-
cipal period of emergence, however, is from about the 25th of July to
the middle of August.

KINDS OF TREES ATTACKED.

The white pine is the tree normally attacked, but the weevil is occa-
sionally found in the terminals or topmost branches of the native and
cultivated spruces, the jack pine, and very rarely in the pitch pine or
other eastern pines. The attack is confined to the small to large sap-
ling and pole stages in the development of the tree.

DISTRIBUTION.

Our records indicate that this weevil follows the natural range of the
white pine from southwestern North Carolina into New Brunswick and
Canada and westward into Wisconsin.

EVIDENCE OF ATTACK.

The first evidence of attack on the living terminals is the exudation
of fresh, clear, and shining drops of resin. Upon closer examination
fresh pinhole-like punctures are found in the bark (fig. 3), and at the
same time the inconspicuous beetles may be found on the terminal ; but
upon the approach of the observer the beetles will often let go their
foothold and fall to the ground, where they will feign death. In a few
days after the first attack the injured terminals will have the resin
more or less abundant and conspicuous over the greater part of the sur-
face. The first evidence that the terminals are infested with larvae is
the. stunted, unhealthy appearance of the young growth at the tip,
which will gradually die, the needles turning yellowish and later
brownish.

The time of development of the broods to adults will be indicated by
the first appearance of dead tips.

Old work of the weevil is evidenced by the presence of old dead ter-

Fig. 3.— Work of white-pine weevil, showing character of injury, chip cocoons, and pupal cells:
a. Vigorous terminal shoot, showing condition of new growth at time pupae are transforming
to adults; b, 3-year-old top, showing how larvae have migrated from terminal to the 2 and 3
year old internodes; c, chip cocoon and pupal cell, natural size. (Original.)

minals in the forks
of the young trees
(fig. 4), and the re-
sults of their work
will be evident in the
deformed growth,
large forks, and
broad, low crowns of
both young and old
trees (fig. 5).

CHARACTER OF THE
DAMAGE.

The damage and
loss, as affecting the
commercial tree, con-
sists not only in the
death of the terminal
shoots, but in subse-
quent abnormal de-
velopment of the
trees so injured. The
dying of the leading
shoot throws the next
year's growth into the
upper lateral shoots,
which results in a
forked and many-
branched top. Each
branch produces a
vigorous terminal,
and all compete for
leadership in forming
the crown. In suc-
ceeding years the
more vigorous termi-
nals of the topmost
branches are at-
tacked and killed,
causing more branch-
es, and thus effec-
tually preventing the
development of the
normal straight trunk
and symmetrical crown necessary to a tree of commercial value.

Work of white-pine weevil, showing result of killed terminal
shoot in 4-year-old top of small sapling. (Original.)

6

EXTENT OF DAMAGE.

The extent of damage, as affecting natural reproduction, planta-
tions, and tim-
ber of commer-
cial size in the
forest, is difficult
to estimate ; but
it is an impor-
tant item to be
charged to the
losses in com-
mercial growth
of white pine and
is therefore a for-
estry problem
which must de-
mand special at-
tention in the
future manage-
ment of wood-
lots and forests,
wherever the tree
predominates.

FAVORABLE A N D
UNFAVORABLE

CONDITIONS FOR
DESTRUCTIVE
WORK BY THE
WEEVIL.

The most fa-
vorable c o n d i -
tion for serious
injury by this
weevil consists
in a scattering or
open pure stand
of young white
pine where the
growth is healthy
and rapid, such
as is found in
open planta-
tions, in aban-
doned fields, and

Fig. 5.— Work of white-pine weevil, showing result of killed terminal _ ,

shoot in 8-year-old top of large sapling. (Original.) arOUlld the OOr-

ders of dense stands wherever the soil and other conditions are most
favorable for rapid growth.

The unfavorable conditions for injury are slow growth, dense pure
stands, and mixed stands of pine and hardwood.

Under the former conditions the thrifty, vigorous terminals are espe-
cially favored as breeding places for the weevil ; and where these are
killed, the vital energy of the tree is thrown into the lateral branches.
Open stands, therefore, favor the development of large branches and a
spreading crown, while under conditions unfavorable to weevil injury
the terminals are smaller and, even if they are killed, the close stand or
lateral shade will tend to produce an upward -or vertical growth of the
topmost branches, the stronger one taking the lead and soon repairing
the damage.

NATURAL ENEMIES.

Numerous parasitic and predatory insect enemies attack the develop-
ing broods in the terminals. Woodpeckers, also, feed on the matured

Fig. 6.— Barrel for terminal shoots infested by white-pine weevil, with wire screen over end allow-
ing escape of parasites but presenting escape of weevils. (Original.)

larvae, pupa?, and adults. Some of the larvae apparently die from
disease, and when large numbers of them are crowded together the
larger ones appear to feed on the smaller ones, so that on the average
not more than from 3 to 5 per cent of the hatched larvae ever reach
maturity and emerge from the infested terminals. However, each
female is capable of depositing more than one hundred eggs each year
for several years ; thus the depredations are continuous. During some
.years the damage will be slight, while in other years it will be very
severe, the amount of injury depending on the number of adults that
survive and the conditions presented for their attack and development.

METHODS OF CONTROL.

It will be seen that in the successful control of this pest, as in the
control of forest insects in general, much depends on special features in

8 -

the general methods of forest management which will bring about
unfavorable conditions for injury and thus prevent loss.

It will also be seen how important it is to know the principal facts
in regard to the life history and habits of the insect, in order to secure
the best results from methods of management and of direct control.

Heretofore this species has been confused with another species with
very different habits, and some of the published data and recommen-
dations based on such confusions are of no value.

The white-pine weevil rarely, if ever, passes the winter in the termi-
nals. The present evidence indicates that it never breeds in the thick
bark on the trunks and stumps of the white pine or other pines ; thus
it can not be trapped in the trunks of felled and girdled pine.

DESTRUCTION OF THE BROODS.

The only practical method of destroying the weevil appears to be the
treatment of the infested terminals, and to secure the best results spe-
cial attention must be given to certain important details.

If the infested terminals are cut or broken during June and July and
burned, the broods of the weevil will be effectual!}' destroyed, but vast
numbers of natural enemies will also be destroyed. A better method
is to collect the terminals during the first half of July before the beetles
begin to emerge and to place them in tight barrels securely covered
with wire fly-screen netting on one or both ends (see fig. 6). The bar-
rels should be left in the groves, so that the parasites and other
enemies may escape, while the beetles perish. After the 1st of October
the weevils will all be dead, and the netting may then be removed,
although the barrels with their contents should be left until the follow-
ing June to allow the escape of the later developing and larger parasites.
The barrel should not be placed in a position to collect rain. It is
necessary, however, if this method be adopted, that it be repeated two
or three years in succession in the same locality, in order to catch the
successive broods from the old parent beetles that live over from pre-
ceding years.

NOTE.

The statements and recommendations in this circular are based on recent
observations and investigations by the author and by Field Assistant W, F. Fiske,
and serve as a partial revision of what has hitherto been published.

Approved :

James Wilson.

Secretary of Agriculture.

Washington, D. C. May 21, 1907.

O